When you push on the Power Button the Power led lights ON or NOT, your Acer Aspire 4540 won’t start up, and there is no display just a black screen. Possible problem and the fixes steps:

Battery has no charge left + AC adapter failed; you press the power button on laptop Acer Aspire 4540 nothing happens, laptop won’t turns on and there is no display, the battery has no charge left, the motherboard doesn’t receive any power, laptop cannot turn on. You plug in the AC adapter but that doesn’t help, your laptop Acer Aspire 4540 still won’t power on, there is a chance you have failed AC adapter. In this case try with another charger or check AC adapter with a Multimeter. If it’s dead, replaced with a new one, (How to check AC adapter with Multimeter).

Power circuit in wrong state or Over volt protection trips; you press the power button but nothing happens, laptop Acer Aspire 4540 won’t turns on and there is no display just a black screen, your laptop has static electric charge made power circuit in wrong state. Unplug AC adapter, take out the battery and hold down power button for 30 seconds, the static charge will dissipate. Plug in the AC Adapter and turn on your laptop Acer Aspire 4540. This should restore the system to normal operating mode.

Screen faulty or bad video cable connection; laptop Acer Aspire 4540 turns on, but screen is black, with Power led lights ON. Test the laptop with an external monitor connected to the HDMI port, VGA port, press the appropriate key to switch to it. If the external monitor works fine and load the operation system, most likely you have a faulty screen or bad video cable connection. Check them and replace the faulty one.

Power button failed; the charge led lights on when you plug in the AC adapter, but laptop won’t turn on when you press the power button. Probably you have a Power button failure. The Acer Aspire 4540 Power button has to be repaired or replaced; you can short the power button borne with conductor wire to see if laptop turns on, (How to Test Power Button).

Hardware failure; the laptop powers on, but there is no display just black screen with Power led lights ON or your laptop Acer Aspire 4540 stock on logo or restart. In this case, it’s possible one of the Hardware failed. You can try to disassemble the laptop to bare minimum and try to reseat the hardware one by one and power on the laptop every time you reseat a hardware, to know the failed one, replace the faulty hardware,